Shiny Pikachu Available Worldwide in Pokemon Go
These shiny Pokemon were first available to trainers who participated in the "Pikachu Outbreak" event in Yokohama, Japan. The event started about two weeks ago on August 9, ended just a few days ago on August 15.
The three Shiny Pikachu forms are joining the ranks of Shiny Magikarp and Shiny Gyrados as the only shinies available in the game at this time.
When you encounter these Pokemon on the world map, you will know that they are Shiny versions if they appear to be slightly darker or more orange than their usual forms.
There are no advantages to having a shiny Pokemon, but they are rarer than the normal version. So that makes them high-valuable collectibles for those who really want to catch 'em all.